1. Field of the Invention
The present invention relates to an image coding-decoding method, an image coding-decoding system, an image coder, an image decoder, and a storage medium, and more particularly to an image coding-decoding method and system for restoring a processed image by performing multiresolution coding and decoding processes in addition to image processing, an image coder and decoder used in the image coding-decoding system, and a storage medium recording a program for making a computer execute the image coding-decoding method.
2. Description of the Related Art
Radiation recording-reproducing systems have been proposed in Japanese Unexamined Patent Publication Nos. 55(1980)-12429, 56(1981)-11395, 55(1980)-163472, 56(1981)-164645, 55(1980)-116340, etc. These systems utilize an accumulable phosphor (stimulatable phosphor), which stores part of radiation energy when illuminated with radiation, such as X-rays, etc., and emits photostimulated luminescent light according to the amount of the stored radiation energy when illuminated with excitation light such as visible light, etc. The radiation image of a subject, such as a human body, etc., is temporarily photographed and recorded on an accumulable fluorescent sheet. The accumulable fluorescent sheet with the radiation image emits photostimulated luminescent light when scanned with excitation light such as laser light, etc. The obtained photostimulated luminescent light is photoelectrically read and converted to an electrical image signal by photoelectric reading means such as a photomultiplier, etc. Based on the image signal, the radiation image of the subject is output as a visible image to a recording material such as a photosensitive material, etc., or to a cathode-ray tube (CRT) display unit, etc.
It is common practice that in the case where an image acquired by the aforementioned image reader is output on a CRT monitor or film and utilized for diagnosis, the acquired image is subjected to image processing, such as a gray level transformation process, a frequency enhancement process, a dynamic-range compression process, etc., so that it becomes an image suitable for observation.
On the other hand, a multiresolution coding method has recently been proposed as a high-efficient image coding method. In this method, a multiresolution transformation process is performed on an image signal which represents an image acquired by an image reader, a digital still camera, etc., in order to obtain hierarchical data for each resolution level which represents an image having a resolution of ½P (where P is an integer) of the acquired image and a size of ½2P of the acquired image. The data stored in all resolution levels is coded and compressed, whereby coded data with compressed redundancy is obtained. The coded data is stored. In addition, it is known that the aforementioned multiresolution transformation process utilizes, for example, wavelet transformation utilized in JPEG 2000, Laplacian pyramid transformation utilized in the Flash Pix file (proposed by Eastman Kodak), or Gaussian pyramid transformation.
If an image is stored by the aforementioned multiresolution coding method, the amount of stored information will be reduced and therefore storage efficiency will be enhanced, compared with the case of storing the original data. In addition, in the case where, based on coded data (image signal) subjected to the aforementioned multiresolution transformation process, an image is output as a visible image on a CRT monitor, film, etc., the image is restored and used in the same resolution level or image size as the acquired image, or in an intermediate resolution level or different size (enlarged or reduced size) from the size of the acquired image, depending on the application. Because of this, data transfer or image processing can be performed in the resolution level or image size required for actual reproduction and output. Particularly, if the aforementioned image processing, etc., is performed with a reduced image having a low-resolution level, the entire system can be operated at high speeds with high efficiency. For instance, in the case where there is a need to reproduce a high-quality image, as in the case of printers, a high-quality image with the same resolution and same size as the acquired image can be reproduced by performing image restoration, based on data stored in all resolution levels which represent images up to the highest-resolution level. On the other hand, when reproducing an image whose resolution is not so high as that of an image output by a printer, as in the case of CRT monitors, an image with a lower resolution and a smaller size than the acquired image can be reproduced based on data stored in a resolution level representing the reduced image, and if further necessary, an image with a lower resolution and a smaller size than the acquired image but suitable for the resolution and screen size of a CRT monitor can be reproduced by enlargement or reduction.
In the case where an image is reproduced based on the coded data stored by use of the aforementioned multiresolution coding method, however, the coded data has to be decoded to the original image signal, and furthermore, image reproduction has to be performed after a desired image processing. Thus, there is a problem that image reproduction will be time-consuming, by in direct correspondence to the extent to which the decoding process is required.